The eyes are windows into the mind, and this research into what jumping spiders look at and why required a clever device that performs eye tracking, but for jumping spiders. The eyesight of these fascinating creatures in some ways has a lot in common with humans. We both perceive a wide-angle region of lower visual fidelity, but are capable of directing our attention to areas of interest within that to see greater detail. Researchers have been able to perform eye-tracking on jumping spiders, literally showing exactly where they are looking in real-time, with the help of a custom device that works a little bit like a miniature movie theatre.
To do this, researchers had to get clever. The unblinking lenses of a spider’s two front-facing primary eyes do not move. Instead, to look at different things, the cone-shaped inside of the eye is shifted around by muscles. This effectively pulls the retina around to point towards different areas of interest. Spiders, whose primary eyes have boomerang-shaped retinas, have an X-shaped region of higher-resolution vision that the spider directs as needed.
So how does the spider eye tracker work? The spider perches on a tiny foam ball and is attached — the help of a harmless and temporary adhesive based on beeswax — to a small bristle. In this way, the spider is held stably in front of a video screen without otherwise being restrained. The spider is shown home movies while an IR camera picks up the reflection of IR off the retinas inside the spider’s two primary eyes. By superimposing the IR reflection onto the displayed video, it becomes possible to literally see exactly where the spider is looking at any given moment. This is similar in some ways to how eye tracking is done for humans, which also uses IR, but watches the position of the pupil.
In the short video embedded below, if you look closely you can see the two retinas make an X-shape of a faintly lighter color than the rest of the background. Watch the spider find and focus on the silhouette of a tasty cricket, but when a dark oval appears and grows larger (as it would look if it were getting closer) the spider’s gaze quickly snaps over to the potential threat.
Feel a need to know more about jumping spiders? This eye-tracking research was featured as part of a larger Science News article highlighting the deep sensory spectrum these fascinating creatures inhabit, most of which is completely inaccessible to humans.
A cool thing about some insects (and if I recall correctly spiders do this too) is that they can derive color information even though they only have monochromatic photoreceptors. By separately processing information at the edges of objects in their vision they can derive color information because the angle of refraction is different across wavelengths.
So we no longer can for sure say whether other animals have color vision or not purely as a function of how many types of photoreceptors they have.
The photoreceptors are sensitive to a rather narrow range of colors, so it’s not really color vision. It may sense whether the one color is leaning towards longer or shorter wavelengths.
Jumping spiders do have color receptors. In fact, they see colors better than humans, as they are tetrachromats.
Their primary eye resolution is high enough to be able to make out the moon. (But probably not any details.) But those eyes only have a 15° field of view, as they rely on the secondary fixed eyes for wide-angle views. Some spiders are transparent, and you can see their internal eyes move here: https://www.youtube.com/watch?v=gvN_ex95IcE
(Jumping spiders always seem fascinated by camera lenses. I have a pet theory that they find circles interesting, as they remind them of other jumping spider eyes — their form of pareidolia. Sadly, it’s more likely that they’re just big and close. There are many videos of spiders jumping onto camera lenses, which are reliably hilarious.)
They’ll also chase laser pointers. https://www.nationalgeographic.com/animals/article/jumping-spiders-moon-stars-astronomy
Whoa, that video of a transparent spider is wild.
Oh, wow, laser pointers? That’s fantastic. I’ve got to try that out next time I see one!
And screen cursors…In the 80s and 90s, my lab at a large Seattle based aerospace company studied insect based vision. Jumping spiders, dragonflies and mantis shrimp were my favorites.
It would be interesting o go the other way and use a camera to look into a camera lens and see what the spider sees that causes it to jump towards the lens. I would imagine it sees a magnified view of the camera sensor.
Not only insects, octopus also can see in colors with monochromatic photoreceptors and use refraction artefaxts.
Hey how come I can’t move… oooohhh that looks tasty. OMG what is that!!!!
These little guys are amazing!
https://www.frontiersin.org/articles/10.3389/fpsyg.2020.568049/full
There’s another good article from New Scientist in 2006 here: https://rifters.com/real/articles/Sinclair%20ZX80%20spiders.pdf (That’s Peter Watts’ website; he used _Portia labiata_, the spider being discussed, in one of his compulsively readable but incredibly depressing novels. Adrian Tchaikovsky also used them in _Children of Time_, which is much more cheerful.)
I recently got interested in jumping spiders and now have a couple in enclosures on my desk in my home office. They’re fascinating to watch. They’re active, visual hunters that will turn to watch you if they think you’re doing anything interesting. Mine aren’t very bright compared to _Portia_ but they still show a number of complex behaviours; watching them hunt down flies is always satisfying, especially during long boring meetings, and when I watch them pottering around their hides doing maintenance it’s very hard not to think that there’s some kind of mind at work. The two big eyes makes them easy to anthropomorphise, too.
Here’s one of mine, a _Marpissa muscosa_, drinking from a cotton bud: https://old.reddit.com/r/spiders/comments/jpy0uf/i%C5%A1ten_drinking/
BTW, thanks for the link to that paper — it was super interesting! Dense but highly readable, if other people are put off by the wall of text. I haven’t come across the Creature classification before, but it makes a load of sense.
I don’t think that little dude could catch a cricket – maybe RIDE one. I somehow doubt it’s looking at the cricket shadow because it looks like a cricket.
Jumping spiders are quite intelligent for a spider, demonstrating quite complex situation dependent behaviour and even some problem solving and planning in some species. In that situation with only a black silhouette and no other cues it’s likely the spider is attempting to evaluate the potential prey – predatable size, jumpable distance, actually an insect not just a two dimensional black shape that looks like one etc.
I wonder about size difference. Here’s a picture I snapped in my back yard a few years ago. This bug-scale equivalent of a tiger had bagged themselves a (much larger than them) damselfly. https://imgur.com/wwbhfuO
I dispizders, them and the webs they pee allover the place. Get the vacuum out! The only web I want is WWW. But jumping spiders don’t make a mess of webs and clean up afterwards. I had one on the wall and lightly tapped the wall less than an inch in front of it’s eyes it didn’t move a day later it hadn’t moved, later that day it was gone.
One wonders how the spiders react when their ‘home movie’ is interrupted by the inevitable advertisement.
Are they intelligent enough to click the ‘Skip Ads >|’ button?